Assessing the accuracy of remotely sensed fire datasets across the southwestern Mediterranean Basin

Luiz Felipe Galizia,Marcos Rodrigues,Thomas Curt,Renaud Barbero

doi:10.5194/nhess-21-73-2021

Abstract

Abstract. Recently, many remote-sensing datasets providing features of individual fire events from gridded global burned area products have been released. Although very promising, these datasets still lack a quantitative estimate of their accuracy with respect to historical ground-based fire datasets. Here, we compared three state-of-the-art remote-sensing datasets (RSDs; Fire Atlas, FRY, and GlobFire) with a harmonized ground-based dataset (GBD) compiled by fire agencies monitoring systems across the southwestern Mediterranean Basin (2005–2015). We assessed the agreement between the RSDs and the GBD with respect to both burned area (BA) and number of fires (NF). RSDs and the GBD were aggregated at monthly and 0.25∘ resolutions, considering different individual fire size thresholds ranging from 1 to 500 ha. Our results show that all datasets were highly correlated in terms of monthly BA and NF, but RSDs severely underestimated both (by 38 % and 96 %, respectively) when considering all fires > 1 ha. The agreement between RSDs and the GBD was strongly dependent on individual fire size and strengthened when increasing the fire size threshold, with fires > 100 ha denoting a higher correlation and much lower error (BA 10 %; NF 35 %). The agreement was also higher during the warm season (May to October) in particular across the regions with greater fire activity such as the northern Iberian Peninsula. The Fire Atlas displayed a slightly better performance with a lower relative error, although uncertainty in the gridded BA product largely outpaced uncertainties across the RSDs. Overall, our findings suggest a reasonable agreement between RSDs and the GBD for fires larger than 100 ha, but care is needed when examining smaller fires at regional scales.

Highlights

Vegetation fires are a common and destructive hazard in the southwestern Mediterranean Basin
We sought to provide a solid answer to the following questions. (i) Are remote-sensing datasets capturing the actual pattern of fire occurrence and burned area? (ii) To what extent is their accuracy dependent on fire size? To answer these questions, we examined the agreement between remotely sensed and ground-based fire datasets aggregated at monthly and 0.25◦ resolutions across a range of individual fire size thresholds (1 to 500 ha)
We evaluated the ability of remotesensing datasets (RSDs) to reproduce the temporal and spatial patterns of fire activity observed in the ground-based dataset (GBD) by fitting ordinary least squares (OLS) linear regressions and using different metrics (OLS slope, R2 correlation, and relative error)

Summary

Introduction

Vegetation fires are a common and destructive hazard in the southwestern Mediterranean Basin. The Mediterranean fire regime is dominated by human-caused ignitions (Ganteaume et al, 2013), with most of the total burned area (BA) linked to a limited number of large fires during the summer (Turco et al, 2016). These large fire events are facilitated by dry conditions and high temperatures, which are both expected to increase in the future under climate change (Dupuy et al, 2020; Ruffault et al, 2020; Turco et al, 2018a). This is true in Europe where the lack of data sharing, as well as the lack of consistent quality-control procedures of national ground-based fire datasets, has hampered the analysis of fire regimes across broader regional or conti-

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Conclusion